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Gollapudi BB, Rushton EK. Mutagenicity evaluation of methyl tertiary- butyl ether in multiple tissues of transgenic rats following whole body inhalation exposure. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2024. [PMID: 39011993 DOI: 10.1002/em.22616] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Accepted: 06/21/2024] [Indexed: 07/17/2024]
Abstract
Methyl tertiary-butyl ether (MTBE) is used as a component of motor vehicle fuel to enhance combustion efficiency and to reduce emissions of carbon monoxide and nitrogen oxides. Although MTBE was largely negative in the in vitro and in vivo genotoxicity studies, isolated reports of positive findings along with the observation of tumors in the rat cancer bioassays raised concern for its in vivo mutagenic potential. To investigate this, transgenic male Big Blue Fischer 344 rats were exposed to 0 (negative control), 400, 1000, and 3000 ppm MTBE via whole body inhalation for 28 consecutive days, 6 h/day. Mutant frequencies (MF) at the cII locus of the transgene in the nasal epithelium (portal of entry tissue), liver (site of primary metabolism), bone marrow (rapidly proliferating tissue), and kidney (tumor target) were analyzed (5 rats/exposure group) following a 3-day post-exposure manifestation period. MTBE did not induce a mutagenic response in any of the tissues investigated. The adequacy of the experimental conditions to detect induced mutations was confirmed by utilizing tissue samples from animals treated with the known mutagen ethyl nitrosourea. These data provide support to the conclusion that MTBE is not an in vivo mutagen and male rat kidney tumors are not likely the result of a mutagenic mode of action.
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Thompson CM, Aardema MJ, Heintz MM, MacGregor JT, Young RR. A review of mammalian in vivo genotoxicity of hexavalent chromium: implications for oral carcinogenicity risk assessment. Crit Rev Toxicol 2022; 51:820-849. [DOI: 10.1080/10408444.2021.2000934] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Suh M, Wikoff D, Lipworth L, Goodman M, Fitch S, Mittal L, Ring C, Proctor D. Hexavalent chromium and stomach cancer: a systematic review and meta-analysis. Crit Rev Toxicol 2019; 49:140-159. [DOI: 10.1080/10408444.2019.1578730] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Mina Suh
- ToxStrategies, Inc, Mission Viejo, CA, USA
| | | | - Loren Lipworth
- Vanderbilt University Medical Center, Nashville, TN, USA
| | - Michael Goodman
- Emory University Rollins School of Public Health, Atlanta, GA, USA
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Dose-dependence of chemical carcinogenicity: Biological mechanisms for thresholds and implications for risk assessment. Chem Biol Interact 2019; 301:112-127. [DOI: 10.1016/j.cbi.2019.01.025] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/11/2019] [Accepted: 01/25/2019] [Indexed: 12/19/2022]
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Thompson CM, Young RR, Dinesdurage H, Suh M, Harris MA, Rohr AC, Proctor DM. Assessment of the mutagenic potential of hexavalent chromium in the duodenum of big blue® rats. Toxicol Appl Pharmacol 2017; 330:48-52. [DOI: 10.1016/j.taap.2017.07.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Revised: 07/01/2017] [Accepted: 07/03/2017] [Indexed: 02/07/2023]
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Nohmi T, Masumura K, Toyoda-Hokaiwado N. Transgenic rat models for mutagenesis and carcinogenesis. Genes Environ 2017; 39:11. [PMID: 28174618 PMCID: PMC5289047 DOI: 10.1186/s41021-016-0072-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2016] [Accepted: 12/08/2016] [Indexed: 01/18/2023] Open
Abstract
Rats are a standard experimental animal for cancer bioassay and toxicological research for chemicals. Although the genetic analyses were behind mice, rats have been more frequently used for toxicological research than mice. This is partly because they live longer than mice and induce a wider variety of tumors, which are morphologically similar to those in humans. The body mass is larger than mice, which enables to take samples from organs for studies on pharmacokinetics or toxicokinetics. In addition, there are a number of chemicals that exhibit marked species differences in the carcinogenicity. These compounds are carcinogenic in rats but not in mice. Such examples are aflatoxin B1 and tamoxifen, both are carcinogenic to humans. Therefore, negative mutagenic/carcinogenic responses in mice do not guarantee that the chemical is not mutagenic/carcinogenic to rats or perhaps to humans. To facilitate research on in vivo mutagenesis and carcinogenesis, several transgenic rat models have been established. In general, the transgenic rats for mutagenesis are treated with chemicals longer than transgenic mice for more exact examination of the relationship between mutagenesis and carcinogenesis. Transgenic rat models for carcinogenesis are engineered mostly to understand mechanisms underlying chemical carcinogenesis. Here, we review papers dealing with the transgenic rat models for mutagenesis and carcinogenesis, and discuss the future perspective.
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Affiliation(s)
- Takehiko Nohmi
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
- Present address: Biological Safety Research Center, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Kenichi Masumura
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
| | - Naomi Toyoda-Hokaiwado
- Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo, 158-8501 Japan
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Thompson CM, Rager JE, Suh M, Ring CL, Proctor DM, Haws LC, Fry RC, Harris MA. Transcriptomic responses in the oral cavity of F344 rats and B6C3F1 mice following exposure to Cr(VI): Implications for risk assessment. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2016; 57:706-716. [PMID: 27859739 PMCID: PMC5215477 DOI: 10.1002/em.22064] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 10/27/2016] [Indexed: 05/13/2023]
Abstract
Exposure to hexavalent chromium [Cr(VI)] in drinking water was previously reported to increase oral tumor incidence in F344 rats. To investigate the mode of action for these tumors, transcriptomic profiles in oral mucosa samples of F344 rats and B6C3F1 mice were analyzed following exposure to 0.1-180 ppm Cr(VI) for 7 or 90 days. In rats, genome-wide microarray analyses identified no significantly differentially expressed genes (DEGs) at either time point. In mice, 14 and 1 DEGs were respectively identified after 7 and 90 days of exposure. Therefore, relaxed statistical criteria were employed to identify potential DEGs (pDEGs), followed by high-throughput benchmark dose modeling to identify responsive pDEGs for pathway enrichment analysis. This identified 288 and 168 pDEGs in the rat oral mucosa, of which only 20 and 7 showed evidence of dose-response. No significant pathway enrichment was obtained with either pDEG or dose-responsive pDEG lists. Similar results were obtained in mice. These analyses indicate a negligible transcriptional response in the oral mucosa of both species. Comparison of the total number of gene changes in the oral mucosa of rats and mice with responses in the duodenum of animals from the same study demonstrated remarkable dose-response concordance across tissues and species as a function of tissue chromium concentration. The low chromium levels in the oral mucosa and negligible transcript response are consistent with an absence of tissue lesions. These findings are used to compare the merits of linear and nonlinear approaches for deriving toxicity criteria based on the oral tumors in rats. Environ. Mol. Mutagen. 57:706-716, 2016. © 2016 The Authors. Environmental and Molecular Mutagenesis Published by Wiley Periodicals, Inc.
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Affiliation(s)
| | | | - Mina Suh
- ToxStrategies, IncMission ViejoCalifornia
| | | | | | | | - Rebecca C. Fry
- Department of Environmental Sciences and EngineeringGillings School of Global Public HealthChapel HillNorth Carolina
- Curriculum in Toxicology, University of North Carolina at Chapel HillChapel HillNorth Carolina
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Thompson CM, Young RR, Suh M, Dinesdurage HR, Elbekai RH, Harris MA, Rohr AC, Proctor DM. Assessment of the mutagenic potential of Cr(VI) in the oral mucosa of Big Blue® transgenic F344 rats. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2015; 56:621-628. [PMID: 26010270 DOI: 10.1002/em.21952] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 03/07/2015] [Accepted: 03/15/2015] [Indexed: 06/04/2023]
Abstract
Exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water was associated with an increased incidence of oral tumors in F344 rats in a 2-year cancer bioassay conducted by the National Toxicology Program. These tumors primarily occurred at 180 ppm Cr(VI) and appeared to originate from the gingival mucosa surrounding the upper molar teeth. To investigate whether these tumors could have resulted from a mutagenic mode of action (MOA), a transgenic mutation assay based on OECD Test Guideline 488 was conducted in Big Blue(®) TgF344 rats. The mutagenic oral carcinogen 4-nitroquinoline-1-oxide (4-NQO) served as a positive control. Mutant frequency was measured in the inner gingiva with adjacent palate, and outer gingiva with adjacent buccal tissue. Exposure to 10 ppm 4-NQO in drinking water for 28 days increased mutant frequency in the cII transgene significantly, from 39.1 ± 7.5 × 10(-6) to 688 ± 250 × 10(-6) in the gingival/buccal region, and from 49.8 ± 17.8 × 10(-6) to 1818 ± 362 × 10(-6) in the gingival/palate region. Exposure to 180 ppm Cr(VI) in drinking water for 28 days did not significantly increase the mutant frequency in the gingival/buccal (44.4 ± 25.4 × 10(-6)) or the gingival/palate (57.8 ± 9.1 × 10(-6)) regions relative to controls. These data indicate that high (∼180,000 times expected human exposure), tumorigenic concentrations of Cr(VI) did not significantly increase mutations in the gingival epithelium, and suggest that Cr(VI) does not act by a mutagenic MOA in the rat oral cavity.
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Affiliation(s)
| | | | - Mina Suh
- ToxStrategies, Inc., Mission Viejo, California
| | | | | | | | - Annette C Rohr
- Electric Power Research Institute, Palo Alto, California
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